1. Field of the Invention
The present invention relates to an imaging apparatus and a method for driving the imaging apparatus, in particular, to an imaging apparatus equipped with an imaging device having pixels for detecting colors of each of R (red), G (green), B (blue), and a pixel for detecting luminance of W (white), and to a method for driving the apparatus.
2. Description of Related Art
A solid-state imaging device for photographing color images to be mounted on a digital camera has color filters of, for example, Bayer-arrayed three primary colors of R, G and B. However, if only color filters of R, G and B are used, the luminance resolution of a taken image deteriorates when an object has unbalanced color.
Consequently, conventionally, among respective pixels constituting a solid-state imaging device, checkerwise disposed pixels are used as pixels for detecting luminance, and each of color filters of R, G, B three primary colors is formed on respective pixels at remaining checkerwise disposed positions, so that the luminance resolution of a raken image does not depend on the color of an object.
When a digital camera mounted with a solid-state imaging device for photographing a color image, in which pixels for detecting luminance are formed, is used for photographing, for example, moving images, there is such a case that reduced image data are read out from the solid-state imaging device in order to enhance the frame rate. On this occasion, image data are not read out from pixels for detecting luminance, but image data are read out only from pixels for detecting color having a color filter of R, G or B, thereby making image resolution one-half both longitudinally and horizontally with high accuracy. However, in recent solid-state imaging devices, the high pixelation has reached the technical limit and a signal charge amount that can be received with one pixel is very small. Accordingly, when image data are read out from a solid-state imaging device while performing pixel skipping, the luminance sensitivity becomes low.
In order to solve the problem, JP-A-2006-157600 or US 2006/0139468 A1 realizes to obtain images reduced to one-half without lowering the luminance sensitivity by reading out pixel date without performing the skipping when reading out reduced image data from a solid-state imaging device.
Meanwhile, in the solid-state imaging device as disclosed in JP-A-2006-157600 or US 2006/0139468 A1, a filter Y for detecting luminance or a color filter R, G or B is provided on the surface of individual pixel disposed and formed longitudinally and horizontally. The filter Y is provided on the surface of pixels that are disposed at checked positions, and the color filter R, G or B is provided on the surface of pixels that are disposed at remaining checked positions. On the individual surfaces of pixels in even-numbered lines, filters are so arranged as “Y, G, Y, G, . . . ”, and on the individual surfaces of pixels in odd-numbered lines, a line in which filters are so arranged as “R, Y, B, Y, R, . . . ” and a line in which filters are so arranged as “B, Y, R, Y, B, . . . ” are disposed alternately. Then, when image data taken with the solid-state imaging device are used to generate a reduced image having one-half resolution both longitudinally and horizontally, in this embodiment, image data of two pixels adjacent to each other in the longitudinal direction (vertical direction) are added and read out from the solid-state imaging device. Here, the pair of two pixels in the longitudinal direction is constituted of a Y pixel being a pixel having the filter Y and a pixel having any one of color filters R, G and B, and the pair vertically adjacent to a pair constituted of an R pixel and a Y pixel is a pair constituted of a B pixel and a Y pixel. But, when a reduced image is going to be generated at a ratio smaller than one-half in order to further enhancing the frame rate upon reading out image data, the pixel date must be skipped in the vertical direction. Thus, there is a room for further improvement from the standpoint of satisfying both high readout speed at a high frame rate and high image quality.